The present invention relates generally to integrated circuit test sockets and in particular to zero insertion force sockets with low parasitic inductance and capacitance.
Test sockets for integrated circuit devices have long been designed to allow easy and rapid replacement for mass testing and observation. The prior art sockets all share a similar approach of using parallel contact plates to clamp on the test device pins and hold it in place. These contact plates are further connected to the mounting pins that extend below to the testing board.
One example of a commercially available socket is sold by 3M under the tradename ZIP DIP II Socket. The 3M socket uses the parallel opposing plates to electrically connect and hold the test device and has extending contacts for mounting on a board. A similar socket is manufactured by Textool Products, Inc., and also clamps the contact plates on the device lead pins. Yet another socket that clamps the device leads is the Actuated Life Socket 900 Series marketed by AUGAT.
The use of opposing contact plates to hold the device pins and of leads connected to the contact plates extending to the testing board create two inherent critical problems that affect the reliability and accuracy of the device test results. First, the two opposing contact plates generate parasitic capacitance that interferes with the testing process. Second, the extended leads lengthen the contact path between the device pins and the test socket thereby creating parasitic inductance, also affecting the test results.
Though parasitic capacitance and inductance might be eliminated by finding an alternative contact system, none have yet been shown that avoid using opposing contact plates for holding the device or reduce the contact lead path between the test device and testing board. Though existing sockets can hold a test device in place securely during testing with easy removal and rapid replacement of the device, no socket has been able to minimize either parasitic capacitance or inductance, or both.
Another problem with the available prior art devices is their complicated method of holding the test device. Contact plates can lose their spring and can lead to weak electrical contact, while extended leads can break requiring replacement.